This application is based upon and claims priority of Korean Patent Application No. 00-28990 filed May 29, 2000 in the Korean Industrial Property Office, the contents being incorporated herein by reference.
1. Field of the Invention
The present invention relates to an optical pickup for an optical disc with a land and groove structure, and more particularly, to an apparatus generating a seek direction detection signal, irradiating a main light beam and a sub-light beam having a predetermined optical aberration on a certain track of the optical disc, and detecting the seek direction of a light spot formed on the optical disc and the relative positions of the center of the light spot and the center of the certain track on the optical disc with respect to each other.
2. Description of the Related Art
Generally, an optical pickup optically records information on or reproduces information from an optical disc such as a recordable and reproducible RAM type optical disc having a land and groove structure. Such an optical pickup includes a light source emitting a laser light beam, an objective lens focusing the light beam emitted from the light source on an optical disc, thereby allowing a light spot to be formed on the optical disc, a photodetector receiving light reflected from the optical disc and detecting an information signal and an error signal, and a signal processor processing the detected signals.
A conventional apparatus for generating a seek direction detection signal for a light spot formed on an optical disc by an optical pickup, as shown in FIGS. 1 and 2, includes a grating (not shown) for diffracting and branching a light beam radiated from a light source to simultaneously irradiate light beams on a track which information is recorded on or reproduced from and an adjacent track, an photodetector and a signal processor.
Referring to FIG. 1, lands and grooves are alternately formed throughout a RAM type optical disc 1 and signal marks 1a are formed on the lands and grooves. When information is recorded on or reproduced from the optical disc 1, light branched by the grating forms a spot on the optical disc 1. Specifically, a main light beam Bm forms a spot on a track for recording or reproducing information signal mark 1a, and a first or second sub light beam Bs1 and Bs2 leading or following the main light beam Bm by a predetermined phase angle forms a spot on the optical disc 1, the center of the spot being displaced from the center of the spot of the main light beam Bm by xc2x1xc2xd track pitch in the radial direction of the optical disc 1 with respect to the main light beam Bm.
Referring to FIG. 2, the photodetector includes a main photodetector 2a for receiving the main light beam Bm reflected from the optical disc and first and second sub-photodetectors 2b and 2c receiving the first and second light beams Bs1 and Bs2, respectively. Here, the main photodetector 2a is composed of two split plates A and B which are split in the radial direction of the optical disc, and each of the two split plates A and B independently receives a light beam. The first and second sub-photodetectors 2b and 2c are composed of two split plates C and D and two split plates E and F, respectively, which are split in the radial direction of the optical disc.
The signal processor includes a plurality of differential amplifiers 3, 4, 5, and 6 for differentially amplifying signals detected by the main photodetector 2a and the first and second sub-photodetectors 2b and 2c. A tracking control unit 7 generates tracking control signals such as a track error signal and a track cross signal from the signals received from the differential amplifiers 3, 4, 5, and 6. An objective lens driver 8 actuates an objective lens based on the tracking control signals received from the tracking control unit 7. Here, a push-pull signal Md detected by the main photodetector 2a is used as a track error signal (TES).
Since each of the first and second sub-light beams Bs1 and Bs2 is displaced from the main light beam Bm by xc2x1xc2xd track pitch, push-pull signals S1d and S2d from the first and second sub-photodetectors 2b and 2c, respectively, output during track cross have phase differences of xc2x190xc2x0 from the push-pull signal Md. Accordingly, a track cross signal (TCS) is obtained using the differential signal S1d-S2d of the push-pull signals S1d and S2d and the push-pull signal Md detected by the main photodetector 2a. A seek direction detection signal is generated from the track cross signal.
The conventional apparatus for generating a seek direction detection signal can simply detect a track cross signal using three beams. However, because the first and second sub-light beams Bs1 and Bs2 are arranged to precede or succeed the main light beam Bm while being displaced from the main light beam Bm, a problem of cross-erasing of an adjacent track signal occurs on the RAM type optical disc.
Various objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
The present invention has been made to overcome the abovementioned problems of the related art, and accordingly, it is an object of the present invention to provide an apparatus for use with an optical disc, including: an optical branching unit irradiating a main light beam and a sub-light beam, wherein the sub-light beam includes an optical aberration in a direction on a track of the optical disc; a photodetector including a plurality of portions receiving and processing the main light beam and a plurality of portions receiving and processing the sub-light beam; a track error signal detector detecting a track error signal from the portions receiving the main light beam; a track cross signal detector detecting a track cross signal from the portions receiving the main light beam and from the portions receiving the sub-light beam; and a signal processor comparing the track error signal with the track cross signal to detect a seek direction of a light spot formed on the optical disc.
Furthermore, it is another object of the present invention to provide for an apparatus for use with an optical disc, including an optical disc; a light source; an optical branching unit branching incident light into a main light beam and a sub-light beam, forming a main light spot and a sub-light spot, the sub-light spot including optical aberration in a radial or tangential direction of the optical disc; a main photodetector including a plurality of receiving portions receiving and photoelectrically converting the main light beam reflected from the optical disc; a sub-photodetector including a plurality of receiving portions receiving and photoelectrically converting the sub-light beam reflected from the optical disc; a track error signal detector detecting a track error signal from the receiving portions of the main photodetector; a track cross signal detector processing output signals from the receiving portions of the main photodetector and from the receiving portions of the sub-photodetector to detect a track cross signal; and a signal processor comparing the track error signal with the track cross signal to detect a seek direction.